在把旧的温树 app带给世界森林基金时,兰经。 我认为,必须牢记的是,世界森林论坛通过在观点模式与对事件的看法之间发出信号(即:< 守则> 指明了PropertyChanged.PropertyChanged、 INotificationDataErrorInfo.ErrorsChanged等)。 我解决这一问题的办法就是采取这一榜样,并以此为榜样。 我认为模式:
/// <summary>
/// Occurs before the record is deleted
/// </summary>
public event CancelEventHandler DeletingRecord;
/// <summary>
/// Occurs before record changes are discarded (i.e. by a New or Close operation)
/// </summary>
public event DiscardingChangesEvent DiscardingChanges;
然后可以听取这些活动的意见,如有必要,则促使用户参加,如果主动取消活动。
请注意,<代码>CancelEventHandler按框架界定。 但是,关于<代码>丢弃Changes,你需要一个三州的成果,表明你想如何操作(即,除改动、抛弃改动或取消你正在做的工作)。 为此,我刚刚发言:
public delegate void DiscardingChangesEvent(object sender, DiscardingChangesEventArgs e);
public class DiscardingChangesEventArgs
{
public DiscardingChangesOperation Operation { get; set; } = DiscardingChangesOperation.Cancel;
}
public enum DiscardingChangesOperation
{
Save,
Discard,
Cancel
}
I tried to come up with a better naming convention, but this was the best I could think of.
因此,将其付诸行动,就象:
ViewModel (this is actually a base class for my CRUD-based view models):
protected virtual void New()
{
// handle case when model is dirty
if (ModelIsDirty)
{
var args = new DiscardingChangesEventArgs(); // defaults to cancel, so someone will need to handle the event to signal discard/save
DiscardingChanges?.Invoke(this, args);
switch (args.Operation)
{
case DiscardingChangesOperation.Save:
if (!SaveInternal())
return;
break;
case DiscardingChangesOperation.Cancel:
return;
}
}
// continue with New operation
}
protected virtual void Delete()
{
var args = new CancelEventArgs();
DeletingRecord?.Invoke(this, args);
if (args.Cancel)
return;
// continue delete operation
}
View:
<UserControl.DataContext>
<vm:CompanyViewModel DeletingRecord="CompanyViewModel_DeletingRecord" DiscardingChanges="CompanyViewModel_DiscardingChanges"></vm:CompanyViewModel>
</UserControl.DataContext>
观点:
private void CompanyViewModel_DeletingRecord(object sender, System.ComponentModel.CancelEventArgs e)
{
App.HandleRecordDeleting(sender, e);
}
private void CompanyViewModel_DiscardingChanges(object sender, DiscardingChangesEventArgs e)
{
App.HandleDiscardingChanges(sender, e);
}
两种固定方法属于上诉类别,每个观点都可以使用:
public static void HandleDiscardingChanges(object sender, DiscardingChangesEventArgs e)
{
switch (MessageBox.Show("Save changes?", "Save", MessageBoxButton.YesNoCancel))
{
case MessageBoxResult.Yes:
e.Operation = DiscardingChangesOperation.Save;
break;
case MessageBoxResult.No:
e.Operation = DiscardingChangesOperation.Discard;
break;
case MessageBoxResult.Cancel:
e.Operation = DiscardingChangesOperation.Cancel;
break;
default:
throw new InvalidEnumArgumentException("Invalid MessageBoxResult returned from MessageBox.Show");
}
}
public static void HandleRecordDeleting(object sender, CancelEventArgs e)
{
e.Cancel = MessageBox.Show("Delete current record?", "Delete", MessageBoxButton.YesNo) == MessageBoxResult.No;
}
在这些静态方法中集中使用方言箱,让我们能够轻易地为后来的习俗方言交换。
